This invention relates to control systems, and more specifically to a control system that is particularly suited to be cooperatively associated with a bowl mill for purposes of continuously measuring the fineness and mass (or volume) flow rates of a multiphase, multicomponent fluid, such as coal particles pneumatically transported in air, and based on such measurements is operative to modulate bowl mill classifier settings or other bowl mill control settings in order to achieve an optimization of the process system of which the bowl mill forms a part.
One of the important parameters in many industrial processes is particle size. As such, it has long been known in the prior art to provide devices that are capable of being employed for purposes of effecting measurements of particles. To this end, the prior art is replete with examples of various types of devices that have been used to obtain measurements of particles. In this regard, in many instances discernible differences exist in the technique by which the measurement of the particles is accomplished. The existence of such differences is, in turn, attributable for the most part to the diverse functional requirements that are associated with the specific application in which such devices are designed to be employed. For instance, in the selection of the particular type of device that is to be utilized for a specific application one of the principal factors to which consideration must be given is that of the nature of the substance of which the particle that is to be measured is formed. Another factor to which consideration must be given is that of the nature of the substance in which the particles are present at the time they are being measured. Yet another factor to which consideration must be given is the relative size of the particles that are to be measured.
Some of the techniques that have been utilized heretodate by the prior art for purposes of accomplishing the measurement of particles include acoustical techniques, optical counting techniques, electrical counting techniques, sedimentation techniques, separation techniques and surface measurement techniques. Moreover, the kinds of particles with which such techniques have been sought to be applied for purposes of making measurements of the particles include such particles as blood particles, food particles, chemical particles, mineral particles as well as others. In addition, diverse ones of the techniques to which reference has been had hereinbefore have been sought to be employed for purposes of accomplishing the measurement of particles while the latter are present in a variety of different types of fluid substances such as various types of gases and various types of liquids.
Unfortunately, however, the devices that have been available in the prior art heretofore for purposes of enabling the techniques to be carried out which have been referred to above have been found to be disadvantageously characterized in one or more respects. To this end, where such devices have been sought to be employed in connection with applications involving industrial processes for purposes of generating information relating to particle size that could be utilized to accomplish, as needed, adjustments to the industrial process, it has not been possible through the use of prior art forms of devices to generate the information required in a sufficiently timely fashion and/or with the desired degree of accuracy. Namely, it has proven to take far too long and/or to require far too much effort to generate the desired information pertaining to particle size for this information to be of any significant value insofar as concerns to the utilization thereof for purposes of making timely adjustments to the industrial process. In large measure this is based on the fact that with the prior art devices that have heretofore been available for use for purposes of effectuating particle size measurements it has not been possible to make measurements in situ therewith. As a result, in order to make use of the prior art devices that have been available heretofore there has most often existed a need to collect a sample from the medium in which are present the particles that it is desired to measure, a need to transport this sample to the device that is to be used to accomplish the particle size measurements, a need go actually perform the particle size measurements with the device, and then finally based on the results of the particle size measurements effectuate whatever adjustments must be made to the industrial process in order to ensure that the particles do in fact embody the size that they must have if the particular industrial process from which the particles that were measured were taken is to be successfully operated.
One form of industrial process in which particle size is known to be an important consideration for the successful operation of the process is the combustion of pulverized coal. As regards the combustion of pulverized coal, it has long been known that an essential component of any steam generation system that utilizes pulverized coal as a fuel is the apparatus in which the coal is pulverized in order to render the coal suitable for such usage. Although the prior art is known to have employed various types of apparatus for purposes of accomplishing coal pulverization, one form of apparatus in particular, which has frequently been used for this purpose, is that commonly referred to as a bowl mill by those in the industry. The bowl mill obtains its name principally from the fact that the pulverization, i.e., grinding, of the coal that takes place therewithin occurs on a grinding surface which in configuration bears a resemblance somewhat to that of a bowl.
By way of illustration, reference may be had to U.S. Pat. No. 3,465,971, which is assigned to the same assignee as the present invention, for a showing of a prior art form of bowl mill. This patent contains a teaching of both the nature of the construction and the mode of operation of a bowl mill that is suitable for use for purposes of effecting the pulverization of the coal that is used to fuel a coal-fired steam generator. As taught by this patent, the essential components of such a bowl mill are a body portion, i.e., housing, within which a grinding table is mounted for rotation, a plurality of grinding rolls that are supported in equally spaced relation one to another in a manner so as to coact with the grinding table such that the coal disposed on the surface of the grinding table is capable of being ground, i.e., pulverized, by the rolls, coal supply means for feeding to the surface of the grinding table the coal that is to be pulverized in the bowl mill, air supply means for providing to the interior of the body portion the air that is required for the operation of the bowl mill, and a classifier that is operative to effect a sorting of the coal particles that are entrained in the air stream which flows to and through the classifier.
In order to satisfy the demands of a coal-fired steam generation system of conventional construction for pulverized coal a multiplicity of bowl mills of the type shown in the aforereferenced patent are commonly required to be employed. Further in this regard it is noted that the individual capacity of each of these bowl mills may range up to a capacity of one hundred tons of pulverized coal per hour. In addition to possessing a capability of operating at their maximum capacity, these bowl mills must also have the ability to operate at less than full capacity, i.e., at some percentage thereof, e.g., 25%, 50%, 75%, etc. Accordingly, this fosters a further requirement that the bowl mill be capable of grinding coal particles to the desired fineness regardless of the rate of output at which the bowl mill is operating. Here note is taken of the fact that variations in the output provided from the bowl mill are normally accomplished by varying the amount of coal that is fed to the grinding table, while the speed of rotation of the grinding table is made to remain substantially constant.
The efficient combustion of pulverized coal, particularly as it relates to the use of pulverized coal as a fuel in a steam generation system, requires that the coal particle size be held close to a specified particle size distribution. Typically, for a medium reactivity coal this is 70% passing through 200 mesh, and 1% not passing through 50 mesh. Based on an economic evaluation for a typical 500 MW coal-fired steam generator power plant, it has been determined that through an increase in carbon conversion rate which in turn is achievable by maintaining a specified particle size distribution, it is possible to realize significant savings amounting to hundreds of thousands of dollars on an annualized basis in the cost of operating a power plant of the size to which reference has been had hereinbefore. Obviously, however, the savings that will be actually realized insofar as any specific power plant that is fueled with pulverized coal is concerned by virtue of maintaining the coal particle size close to a specified particle size distribution will be dependent on a number of factors including the reaction kinetics of the coal, i.e., how sensitive the combustion efficiency is to particle size for the specific coal being used, the grindability of the coal, the abrasiveness of the coal, how well and often control is exercised over the bowl mill to maintain the optimum size distribution of the coal particles, and how well the bowl mill is maintained. In every instance, however, maintaining the size distribution of the coal particles close to the optimum should result in some measure of fuel savings.
Other benefits should also flow from the fact that better control is being exercised over the size distribution of the coal particles. In this regard, reference is had to the fact that there should be reduced slagging in the steam generator due to better control over the size distribution of the coal particles. In addition, if deviations are occurring in the size distribution of the coal particles from that which should be present, necessary adjustments can then be made to the classifier settings of the bowl mill so that the proper size distribution of the coal particles will occur. Also, continuous control may be exercised over the operation of the bowl mill through the use of the information garnered from having made coal particle size measurements. Yet another possibility is to utilize the information acquired from the performance of coal particle size distribution measurements for purposes of obtaining an indication of the fuel-to-air ratio in the coal feed pipe by means of which, in a manner well-known to all, the pulverized coal particles are conveyed from the bowl mill to the steam generator wherein the combustion of the pulverized coal particles takes place.
Thus, there has been evidenced in the prior art a need for a new and improved form of control system suitable for use with various types of grinding, crushing, or other kinds of comminuting devices that function to produce a dispersed multiphase, multicomponent fluid such as, by way of exemplification and not limitation, coal, lime, talc and paint pigments. Further, a need has been evidenced for such a new and improved control system which when employed in conjunction with the aforereferenced types of devices enables continuous control to be effected over the size and distribution of the materials that are being ground, crushed, or otherwise comminuted in the devices. Moreover, a need has been evidenced for such a new and improved control system which makes use of a measurement technique that is nonintrusive such that wear is thereby minimized. In addition, such a new and improved control system also should desirably be characterized by the fact that the control logic thereof allows for an optimization of the product that is being ground, crushed or otherwise comminuted based on a consideration of such factors as the energy cost and maintenance cost associated with the device's operation as well as based on a consideration of how sensitive the downstream process in which the product is intended to be utilized is to the product's characteristics. To this end, such a new and improved control system desirably would not necessarily be operated on a continuous basis for long periods of time, but rather through the use of the appropriate forms of jigs and fixturing would possess the capability of being employed periodically with different devices at the same facility, or with different devices at different facilities.
It is, therefore, an object of the present invention to provide a new and improved control system suitable for use with various types of grinding, crushing or other forms of comminuting devices.
It is another object of the present invention to provide such a control system which is suitable for use with devices of the type that function to produce a dispersed multiphase, multicomponent fluid such as, by way of exemplification and not limitation, coal, lime, talc and paint pigments.
It is still another object of the present invention to provide such a control system which when employed in conjunction with grinding, crushing or other comminuting devices enables continuous control to be effected over the size and distribution of the materials that are being ground, crushed or otherwise comminuted in the devices.
A further object of the present invention is to provide such a control system which makes use of a measurement technique that is nonintrusive such that wear is thereby minimized.
A still further object of the present invention is to provide such a control system that is further characterized by the fact that the control logic thereof allows for an optimization of the product that is being ground, crushed or otherwise comminuted based on a consideration of such factors as the energy cost and maintenance cost associated with the device's operation as well as based on a consideration of how sensitive the downstream process in which the product is intended to be utilized is to the product's characteristics.
A yet still further object of the present invention is to provide such a control system that is operative to detect in a timely fashion equipment failures such as in the case of a bowl mill body liner failures, classifier vane failures, etc.
Yet another object of the present invention is to provide such a control system that is additionally characterized by the fact that the control system does not need to be operated on a continuous basis for long periods of time, but rather through the use of the appropriate forms of jigs and fixturing would possess the capability of being employed periodically with different devices at the same facility, or with different devices at different facilities.
Yet still another object of the present invention is to provide such a control system that is relatively simple to employ as well as being relatively inexpensive to provide.